全文获取类型
收费全文 | 3080篇 |
免费 | 97篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 112篇 |
大气科学 | 369篇 |
地球物理 | 651篇 |
地质学 | 918篇 |
海洋学 | 350篇 |
天文学 | 556篇 |
综合类 | 5篇 |
自然地理 | 235篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 34篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 92篇 |
2017年 | 62篇 |
2016年 | 119篇 |
2015年 | 69篇 |
2014年 | 93篇 |
2013年 | 162篇 |
2012年 | 132篇 |
2011年 | 170篇 |
2010年 | 137篇 |
2009年 | 201篇 |
2008年 | 179篇 |
2007年 | 165篇 |
2006年 | 139篇 |
2005年 | 113篇 |
2004年 | 120篇 |
2003年 | 110篇 |
2002年 | 107篇 |
2001年 | 88篇 |
2000年 | 91篇 |
1999年 | 72篇 |
1998年 | 87篇 |
1997年 | 49篇 |
1996年 | 47篇 |
1995年 | 33篇 |
1994年 | 25篇 |
1993年 | 32篇 |
1992年 | 22篇 |
1991年 | 34篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1973年 | 8篇 |
1971年 | 11篇 |
排序方式: 共有3196条查询结果,搜索用时 0 毫秒
71.
Earthquake motion is one of the extreme loads acting on large dams. Dam owners and regulators must therefore ensure that dams
are safely operated and present minimal risk to the public in case of extreme loads such as floods and earthquakes. Owners
of many dams or officials in charge of dam safety programs may consider comparative assessment of the seismic risk associated
with their dams and establish priorities for detailed evaluation. South Africa has in excess of 100 large state-owned dams
and the characteristics of these dams have been used to perform a basic seismic hazard assessment and rank the vulnerability
of these dams from the lowest to highest. One of the most decisive factors that contributes to the risk of a dam is the wall
type; with gravity and earthfill dams being the most vulnerable to earthquake motion. Another aspect that needs further investigation
is the downstream hazard potential which, if known to a better degree of accuracy, can provide more reasonable estimates of
the risk factors. 相似文献
72.
Influence of spatial variations of microtopography and infiltration on surface runoff and field scale hydrological connectivity 总被引:2,自引:0,他引:2
Willemijn M. Appels Patrick W. BogaartSjoerd E.A.T.M. van der Zee 《Advances in water resources》2011,34(2):303-313
Surface runoff on agricultural fields arises when rainfall exceeds infiltration. Excess water ponding in and flowing through local microtopography increases the hydrological connectivity of fields. In turn, an increased level of hydrological connectivity leads to a higher surface runoff flux at the field boundaries. We investigated the functional hydrological connectivity of synthetical elevation fields with varying statistical properties. For this purpose, we developed an object-oriented ponding and redistribution model to which Philip’s infiltration model was coupled. The connectivity behaviour is determined by the presence of depressions with a large area and spatial organization of microtopography in rills or channels. The presence of microdepressions suppresses the effect of the spatial variation of infiltration properties. Connectivity behaviour of a field with a varying spatial distribution of infiltration properties can be predicted by transforming the unique connectivity function that was defined for a designated microtopography. 相似文献
73.
Hartmut H. Hellmer Monika Rhein Günther Heinemann Janna Abalichin Wafa Abouchami Oliver Baars Ulrich Cubasch Klaus Dethloff Lars Ebner Eberhard Fahrbach Martin Frank Gereon Gollan Richard J. Greatbatch Jens Grieger Vladimir M. Gryanik Micha Gryschka Judith Hauck Mario Hoppema Oliver Huhn Torsten Kanzow Boris P. Koch Gert König-Langlo Ulrike Langematz Gregor C. Leckebusch Christof Lüpkes Stephan Paul Annette Rinke Bjoern Rost Michiel Rutgers van der Loeff Michael Schröder Gunther Seckmeyer Torben Stichel Volker Strass Ralph Timmermann Scarlett Trimborn Uwe Ulbrich Celia Venchiarutti Ulrike Wacker Sascha Willmes Dieter Wolf-Gladrow 《Ocean Dynamics》2016,66(11):1379-1413
74.
Many Precambrian granulite-facies metamorphic complexes contain so-called straight gneisses, which are massive rocks with a clearly pronounced blastomylonitic texture, lineation, and gneissosity. These rocks occur exclusively in high-temperature ductile shear zones, which can develop either during the primary exhumation of rock complexes or during the overprinting by high-temperature dynamometamorphism. The main criterion for distinguishing between these two types of straight gneisses is the configuration of their P-T trajectories, which are recorded in the mineral assemblages in these rocks and their host gneisses. Ductile shear zones developed in Archean granulite gneisses simultaneously with their exhumation, and, hence, their P-T trajectories are segments of decompression and/or isobaric cooling paths. Straight gneisses in Proterozoic polymetamorphic complexes commonly compose high-temperature ductile shear zones overprinted on Archean granulite complexes, and the P-T paths of these rocks are Z-shaped. This means that, at a constant pressure in the middle part of the continental crust, the T min of the older P-T trajectory corresponded to T max of the younger trajectory, and often T max–T min > 100°C. Such ductile shear zones commonly have a strike-slip morphology and can be easily seen in aerial photographs and discerned during structural geological surveying. These zones can overprint older gneisses without any notable thermal effect on the latter. Relations of this type were identified in the granulite complexes of Limpopo in South Africa, Sharyzhalgai in the southwestern Baikal area, and Lapland in the Kola Peninsula. The results of our research propose a solution for the well-known problem of the significant discrepancies between the isotopic ages in high-temperature-high-pressure complexes and the partial or complete distortion of radiogenic isotopic systems under the effect of a newly inflowing metamorphic fluid. The application of geochronologic techniques to these situations is senseless, and only P-T trajectories provide insight into the actual age relations between the discrete tectono-metamorphic stages. It is thus expedient to conduct not only structural studies of metamorphic complexes but also their detailed petrological examination and the calculation of their P-T paths before geochronologic dating. 相似文献
75.
Authigenic carbonates associated with cold seeps provide valuable archives of changes in the long-term seepage activity. To investigate the role of shallow-buried hydrates on the seepage strength and fluid composition we analysed methane-derived carbonate precipitates from a high-flux hydrocarbon seepage area (“Batumi seep area”) located on the south-eastern Black Sea slope in ca. 850 m. In a novel approach, we combined computerized X-ray tomography (CT) with mineralogical and isotope geochemical methods to get additional insights into the three-dimensional internal structure of the carbonate build-ups. 相似文献
76.
AL Mackintosh CC Reed MAI Nunkoo PH King CD van der Lingen 《African Journal of Marine Science》2018,40(3):245-252
The angelfish Brama brama is a mesopelagic species distributed circumglobally in temperate to warm-temperate waters, including continental-shelf-edge and upper-slope waters of the Benguela Current ecosystem. Little is known about the parasite assemblage of Benguela B. brama, with only three parasite taxa having previously been documented from this species in the southern Benguela. This study describes the macroparasites recorded from 35 B. brama collected during research surveys off the west coast of South Africa in 2015 and 2016. A total of six macroparasite taxa were documented, including the nematode Anisakis pegreffii, the copepod Hatschekia conifera, the cestode Hepatoxylon trichiuri, an acanthocephalan from the genus Rhadinorhynchus, a monogenean from the family Diclidophoridae, and an unidentified species. Three of these (He. trichiuri, Rhadinorhynchus sp. and the unidentified species) had not previously been found to infect B. brama. The most prevalent macroparasite taxa were A. pegreffii (94%), the unidentified species (71%) and Ha. conifera (60%). Two of the parasites, Ha. conifera and He. trichiuri, showed seasonal variation in infection, and infection with the latter was positively correlated with host length. These findings increase our knowledge of B. brama biology and contribute to our understanding of the biodiversity of the southern Benguela ecosystem. 相似文献
77.
78.
79.
RudyWijnands † Jon M.Miller Michiel van derKlis 《Monthly notices of the Royal Astronomical Society》2002,331(1):60-70
We report on several pointed Rossi X-ray Timing Explorer observations of the enigmatic low-mass X-ray binary (LMXB) 4U 1957+11 at different X-ray luminosities. The luminosity of the source varied by more than a factor of 4 on time-scales of months to years. The spectrum of the source tends to become harder when its luminosity increases. Only very weak (1–2 per cent rms amplitude, 0.001–10 Hz , 2–60 keV) rapid X-ray variability was observed during the observations. A comparison of the spectral and temporal behaviour of 4U 1957+11 with other X-ray binary systems, in particular LMC X-3, indicates that 4U 1957+11 is likely to be a persistent LMXB harbouring a black hole and it is persistently in the black hole high state. If confirmed, it would be the only such system known. 相似文献
80.